Implantable conformal coil patch electrode with multiple conductive elements for cardioversion and defibrillation

ABSTRACT

Body-implantable leads with open, unbacked (uninsulated) electrode structures having electrical discharge surfaces formed by conductive elements, such as mesh and braid, and preferably coils. The electrode structures can be classified by pattern: (1) loops, (2) linear arrays and (3) radial arrays. The electrodes are located on or near the epicardial surface of the right and left heart.

This application is a divisional application of U.S. patent applicationSer. No. 08/609,215, filed Mar. 1, 1996 now U.S. Pat. No. 5,916,243,which was a continuation of Ser. No. 07/980,843, filed Nov. 24, 1992 nowU.S. Pat. No. 5,496,362, issued Mar. 5, 1996.

FIELD OF THE INVENTION

The present invention relates to the field of implantable conformal coilpatch electrodes with multiple conductive elements for cardioversion,defibrillation and tachyrhythmia therapy.

BACKGROUND OF THE INVENTION

Many different electrodes and electrode configurations have beendisclosed for applying electrical currents to the heart in an attempt toproduce the most efficacious therapy and the least deleteriousshock-induced alteration of myocardial electrophysiologic function.These electrodes have been placed directly on the epicardium of theheart, within the chambers of the right atrium and ventricle, in thecoronary sinus, in the venae proximal to the right heart and in the leftlateral thoracic subcutis. Various physical and electrical combinationsof these electrodes form the electrode configuration.

In the past, the electrode configuration, as described above, mostfrequently employed in patients has been the epicardial patch-to-patchconfiguration as disclosed in U.S. Pat. No. 4,291,707 to Heilman et al.This prior art patch is bulky and relatively inflexible; the electrodeis backed with an insulating layer of silicone rubber that increasestransthoracic defibrillation shock strength requirements as reported byB. B. Lerman and O. C. Deale in Circulation 1990; 81:1409-1414.

More recently, a non-thoracotomy electrode configuration combiningendocardial catheter electrodes with a mesh patch located in the leftaxillary subcutis was disclosed in U.S. Pat. No. 4,662,337 to Heilman,et al.

Still further potential disadvantages of the catheter-patchconfiguration are related to the impedance of the current pathway andthe non-uniformity of the shock-induced electric field. High impedancepathways require higher shock intensities to defibrillate.

Prior art deployable epicardial defibrillation electrodes such as thosedisclosed in U.S. Pat. No. 4,567,900 to Moore undergo shape conversionsubsequent to electrode placement. However, this design is believed tobe fraught with problems related to structural frailty and it does notaddress either the problem of nonuniform current density at theelectrode perimeter or fixation to adjacent tissues.

Additional disadvantages of prior art electrodes include excessive size,insufficient surface area, inefficient conductive discharge surfaces,excessive stiffness, nonconformity to heart shape, fatigue fracture,complex geometries, and complicated and hazardous implantation schemes.

Discussion in U.S. Pat. No. 5,016,645 to Willams et al. and U.S. Pat.No. 4,827,932 to Ideker et al. states either explicitly or implicitlythat nonconductive backing of the defibrillation electrodes is necessaryor beneficial to prevent shunting.

According to the present invention an opposite effect is realized, thatis, unbacked structures require lower shock strengths for defibrillationthan similar structures backed with a nonconductive material.

SUMMARY OF THE INVENTION

The invention relates to the use of body-implantable leads with open,unbacked (uninsulated) electrode structures having electrical dischargesurfaces formed by conductive elements, such as mesh and braid, andpreferably coils. To improve descriptive clarification, the electrodestructures can be classified by pattern formed by the conductivedischarge surfaces: (1) loops, (2) linear arrays and (3) radial arrays.

In the present invention, the electrodes can be located on or near theepicardial surface of the right and left heart, thereby eliminatingproblems associated with other so-called non-thoracotomy electrodeconfigurations involving right heart endocardial electrodes) (e.g.superior vena cava syndrome, pulmonary embolism, endocardialshock-induced tissue damage, endocarditis, physical interference withexisting or future pacing leads) and left thorax subcutaneous patch(es)(e.g. patient discomfort, fatigue fracture, transcutaneous erosion,subcutaneous infection). Electrodes of the present invention may beplaced intrapericardially or extrapericardially.

In general, the present invention is used to efficiently distributeelectrical current from implantable cardioverter/defibrillators fortreatment of ventricular fibrillation or hemodynamically stable orunstable ventricular tachyarhythmias. The present invention solvesseveral problems related to current epicardial (the location ofelectrodes in direct contact with the epimyocardial surface and thoseattached to the parietal pericardium) electrode systems known in the artof implantable defibrillation.

First, the invention reduces inhibition of heart wall motion byexhibiting low stiffness and high flexibility.

Second, the invention reduces therapeutic shock strength requirements bydistributing the current over more efficient conductive dischargesurfaces and thereby reducing shock impedance.

Third, the invention reduces an undesirable increase in transthoracicdefibrillation strength requirements because the open structure (anabsence of any electrically insulative backing material) does notinsulate large portions of both ventricles.

Fourth, the invention exhibits better mechanical fatigue resistance torepeated flexure produced during normal cardiac contraction.

And fifth, the invention, in several embodiments, can be implanted usingso-called "minimally-invasive" approaches involving cardiac accessthrough subxiphoid, subcostal and/or intercostal incisions.

Experimentation with these types of electrodes has shown a significantreduction of shock strength (peak voltage and energy delivered) fordefibrillation compared to the conventional mesh patch as embodied inthe Heilman et al patents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an enlarged view of a section of the heart structure.

FIG. 1B illustrates an insulated lead body and conductive electrodeportion.

FIG. 1C is a sectional view taken along line A--A of FIG. 1B.

FIGS. 2A-2E illustrate linear array conductive electrodes.

FIG. 2F is a side view of the conductive electrode shown in FIG. 2E.

FIGS. 3A-3D illustrate radial array conductive electrodes.

FIGS. 4 to 7 are graphs of test results for six different epicardialelectrode pair configurations which were tested in five pigs.

FIGS. 8A-8D illustrates four conductive loop electrodes of varyingcircumscribed area.

FIGS. 9A, 9A', 9A", 9B, 9C and 9C' illustrate concentric loop conductiveelectrodes.

FIGS. 9D and 9E illustrate a detailed view of a connection of terminalends of coils and connection of adjacent coils to each other.

FIGS. 10A, 10A', 10B and 10C illustrate eccentric loop conductiveelectrodes.

FIG. 10B' is a side view of FIG. 10B.

FIGS. 10D, 10E, 10F and 10G illustrate the method of introducing aconductive electrode to the heart through a tubular applicator locatedin the chest wall.

FIGS. 11A, 11B and 11C illustrate spatially-isolated coil loopconductive electrodes.

FIG. 11A' is a side view of FIG. 11A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In describing a preferred embodiment of the invention illustrated in thedrawings, specific terminology will be resorted to for the sake ofclarity. However, the invention is not intended to be limited to thespecific terms so selected, and it is to be understood that eachspecific term includes all technical equivalents which operate in asimilar manner to accomplish a similar purpose.

By the present invention, conductive electrode structures includeconductive coils forming a conductive discharge surface with an optionalinsulative backing, preferably on one side of the electrode structure.The insulative backing is preferably located on the side of theelectrode structure facing away from the heart.

The conductive electrode structures are formed, for example, (1) as aperipheral loop, optionally having a single radially inwardly extendingconductive element, (2) as linear arrays having conductive elementsextending parallel to or perpendicular to a longitudinal axis of theelectrode structure, (3) as radial arrays having elements extendingradially inwardly or radially outwardly, (4) as concentric loopstructures, (5) as eccentric loop structures, and (6) as spatiallyisolated coil loop structures.

FIGS. 1 to 3 show embodiments of leads with conductive electrodestructures. They are intended to serve as representative examples and donot exhaustively define all parameters meant to be covered by the spiritof the present invention.

Each lead possesses several common characteristics. With reference toFIGS. 1 to 3 and 8 to 11, as shown in FIG. 1B, the lead 1 is formed by aconductive electrode portion 2 (distal) mounted at one terminal end ofan insulated lead body 3 (proximal). The electrode portion 2 is formedby conductive metallic elements (normally helically-wound multifilarcoils) that are electrically common. The electrode portion is designedto be positioned on or near the heart structure, eitherintra-pericardially 4 or extra-pericardially 5, as shown in FIG. 1A.

The metallic coil(s) comprising the electrode portion are eithercontiguous or spatially isolated to form two or more elements that formthe conductive discharge surface. As shown in FIG. 1C, the lumen 6 ofthe metallic coil(s) are filled with silicone tubing 7 or a solidcylindrical form of silicone through which a drawn brazed stranded (DBS)conductor 8 can pass to carry the shock currents to various terminationson the electrode portion.

The electrode portion is energized with an implantable cardioverterdefibrillator pulse generator (not shown) by applying a potential at theproximal terminal pin 9 located at an opposite terminal end of lead body3 from electrode portion 2. Reinforced silicone sheet 10 may be used toform a narrow (<1 cm) rim or boundary that defines the perimeter of theelectrode portion, as in FIGS. 1B (phantom lines) and 2B, for example,on a side of the electrode facing away from the heart. Alternatively,this rim could be formed by a silicone covered coil of appropriatestiffness.

This rim defines the electrode perimeter and serves several purposes:(1) it adds structural stability to the electrode structure by "tieing"together the ends of the conductive elements, and (2) it providesreliable means for securing sutures to the electrode duringimmobilization of the electrode on or near the heart. Alternatively,adequate structural integrity could be imparted to the electrode on aside of the electrode facing away from the heart by means of a fabricbacking 11 (FIGS. 2E and 2F) that is porous and offers negligibleelectrical resistance during therapeutic shocks.

FIG. 1B shows a preferred embodiment of a coil patch electrodeclassified as a "loop". The loop is formed by deflecting the coil 15180° and securing it to the distal end of the lead body 3, here referredto as the root 12 of the loop. An electrically common element 13proceeds radially inward from the root 12 toward the distal extreme ofthe loop, here referred to as the apex 16 of the loop. This inner commonelement 13 carries current from the electrode boundary to inner regionsof the loop thereby increasing the shock field strength in heart tissuenear the center of the loop which otherwise would have experienced weakshock fields. The loop illustrated in FIG. 1B may be a single, multipleconcentric, multiple eccentric or multiple spatially isolated loop asshown in FIGS. 8 to 11.

FIGS. 2A to 2E illustrate various embodiments associated with conformalcoil patches classified as "linear arrays". Linear arrays are grouped bythe orientation of the conductive elements 19 relative to the long axisof the patch: (1) arrays with elements 19 substantially parallel to thelongitudinal axis of the patch are considered "vertical", (FIGS. 2A, 2Band 2C) while (2) arrays with elements 19 substantially perpendicular tothe long axis of the patch are considered "transverse" (FIGS. 2D and2E).

A preferred embodiment is shown in FIG. 2B. The shape of the perimeteris formed by connecting tangent points from two half-circles with equalor unequal radii resulting in a structural boundary that can be referredto as oval (equal radii) or "egg-shaped" (unequal radii). This shapeconforms well to the heart with the large radii end 17 positioned at thecardiac base and the small radii end 18 positioned at the cardiac apex.

With reference to FIG. 2C, three or more conductive coil elements 19 arespatially isolated in an interdigitating pattern as shown. The benefitof interdigitation is related to separating regions of high currentdensity. The optimum number of elements results in lowest shock strengthrequirements for defibrillation.

Unlike embodiments shown in FIGS. 2A, 2B, 2D and 2E, the electrodestructure of FIG. 2C is not bounded by a silicone sheet perimeter.Structural stability is maintained by incorporating biasing means(spring wire or premolded silicone cylindrical forms) within the coilinterior.

FIGS. 3A to 3D show various embodiments of patches classified as "radialarrays". Radial arrays are grouped by the location of the elements: (1)arrays with elements emanating from the center outward to a radiallyoutermost boundary are considered "type 1", (FIGS. 3A and 3D) while (2)arrays with elements proceeding from the boundary partially inward areconsidered "type 2" (FIGS. 3B and 3C). Electrical connection to thedischarge surface is preferably made at the center 20 of the electrodefor "type 1" radial arrays and at the perimeter for "type 2" arrays.

In FIG. 3D a centralized hub portion 53 freely "floats" duringventricular contractions as a consequence of the highly compliantinvoluted conductive elements 54. A perimeter structure 55 provides astable but resilient platform on which the terminal ends 56 of theconductive elements terminate and are bonded, thereby maintainingelement separation.

In general, an open structure (not backed by an insulator) allowsfibrotic isolation of individual elements that reduces the likelihood ofstructural deformation (element migration) during capsular contraction.The perimeter 55 can be constructed from die-cut silicone rubbersheeting, molded in one piece from a suitable material such as siliconerubber or fabricated by covering a coil with silicone tubing. In eithercase, all terminal coil ends 56 are covered with silicone to protectunderlying tissues. The curved coil conductive elements 54 forming theconductive discharge surface proceed in an involuted pattern, from theinner hub 53 to the outer perimeter 55 in a clockwise manner and areuninsulated everywhere except at the hub and at the ends. Alternatively,the elements may "swirl" counterclockwise.

The preferred relaxed electrode shape or element pattern for any of theembodiments shown need not be symmetric. Element lengths, spacings,positions and orientations may be changed to optimize the shock-inducedvoltage gradient distribution in and around the heart.

Embodiments of the present invention may be implanted by several means:(1) direct cardiac exposure through sternotomy or thoracotomy followedby surgical attachment to epicardium or parietal pericardium, (2)physically urging the electrode through an introducing conduitpositioned across the chest wall and in some procedures within thepericardial space using minimally invasive techniques involvingsubxiphoid, subcostal or thoracoscopic-assisted intercostal approaches.Further urging of the electrode through and out of the introducingconduit results in separation of the electrode elements by release ofstrain energy previously imparted to the intra-electrode biasing means.During this electrode shape change, the pericardium assists theelectrode positioning process by acting as a "sock" to bear against theelectrode and direct its translation along the epicardial surface.Stability of the final electrode shape and position is achieved byanchoring the electrode to suitable adjacent tissues with sutures,staples or with an active fixation means (not shown). (3) Alternatively,the electrodes may be implanted and secured to the parietal pericardium(extrapericardial or sometimes referred to as retropericardial) througha small intercostal defect using thoracoscopic assistance. In this case,the ipsilateral lung may be deflated to increase cardiac exposure. Theelectrodes are positioned on or near the heart and secured to theunderlying tissues with sutures or metallic staples.

An in vivo study was performed to determine the influence of coil patchtrace geometry on defibrillation strength requirements in pigs. FIGS. 4to 6 show histograms of mean shock strength requirements described interms of peak voltage, peak current and total energy delivered at pointspredicting 50% defibrillation probability in five pigs. FIG. 7 showsmean system impedance. Error bars denote one standard deviation. Theterm "trace geometry" is a descriptor used to define the shape andorientation of the conductive elements comprising the discharge surfaceof the electrode.

Significant novel features of the invention include, but need not belimited to (1) resilient elements that can be deflected duringintroduction to both technically simplify and decrease the invasivenessof implantation procedures, (2) resilient elements with optimum edgelengths over which shock currents are distributed, thereby reducingnear-field impedance and minimizing peak voltage gradients, (3)electrode construction that does not require an insulative backingthereby producing minimal affect on transthoracic defibrillation shockstrength requirements, (4) electrode structure that reduces peak voltagerequirements for defibrillation by reducing near-field impedance throughdistribution of shock current over a large "phantom area" or "effectiveedge length", (5) electrode structure with interdigitating ends thatspace areas of high current density, (6) electrodes with spatiallyisolated coil elements defining open regions that conform to thedimensional excursions of the heart and thereby maintain intimatecontact with subjacent heart tissue, (7) electrodes with elements thatpossess different resistivities to favorably alter shock-inducedelectric field intensities, (8) electrodes with porous backing thatprovide a substrate for tissue ingrowth and a plane for surgicaldissection, and (9) electrode elements energized in a manner to producedifferent regional potentials on the electrode face.

In FIGS. 8A-8D, different sized loop style conductive electrodes areshown. By varying the length of major axis (a) and the circumference (C)of the loops, the circumscribed surface area (A) is varied.

Concentric loops (normally multi-filar coils) 21 such as those shown aremounted on a three-pronged "skeletal" structure 22 (FIGS. 9A to 9C and9C'). Typically, this structure 22 is fabricated from Dacron® reinforcedsilicone rubber sheeting (0.010-0.030 inch thick, 0.1-0.5 inch wide).Electrodes fabricated in this fashion solve several problems: (1)continuous loops with smooth contours improve structural fatigueresistance, (2) defibrillation shock strength requirements areinsensitive to orientation, (3) structure can be "pre-shaped" to provideradii of curvature that are coincident with typical epicardialcurvatures to facilitate electrode conformation to epicardial surface asshown in FIG. 9B', (4) the high flexural compliance minimally impactsventricular pump function, and (5) shock currents are distributedthrough coiled conductors that have greater surface area per unit lengthcompared to wire mesh conductors used in conventional electrode patches.

Until now, coils have been shown attached to one side of the "skeletal"support structure 22 (FIG. 9A') to provide tangential contact of thecoils 21 with the support structure 22. However, it may be advantageousto produce a structure as shown in FIG. 9A" which depicts the skeletalstructure 22 between the coils 21, lying on an axis coincident with thediameter of the coils. The advantage of such a structure is that itcannot be inadvertently implanted with the conductive discharge surfaceside away from the heart.

Several electrode design factors are believed to influencedefibrillation efficacy: (1) ratio of maximum electrode diameter toheart circumference, (2) number of elements, (3) spatial separation, and(4) means of electrical connection of elements. Two primary means ofelectrical connection exist: (1) connections 23 that cause the elementsto be equipotential as shown in FIGS. 9A, 9B, 9C, and (2) thoseconnections 24 that allow the current to be distributed from theinnermost element to the outermost element as shown in FIG. 9C'.

The reinforced silicone rubber sheet structure 22 that serves as a"skeleton" for the electrode coil elements in many of the designs shownin the figures may be comprised of single or a plurality of arms. Theends of each arm extend beyond the major dimension of the electrodeportion and form a tab 25 (FIG. 9C) thereby providing fixation means tosecure the electrode portion to the underlying tissues with sutures orstaples. Chronic fixation to tissues at these peripheral points may befurther enhanced by incorporation of a suitable porous material 26bonded to the tab 25 or to other areas along the "skeletal" arm. Theporous material may be Dacron or other porous material that promotesstable tissue ingrowth.

With reference to FIGS. 9D and 9E, ends 25, 25' of the coil 21 aredeflected, closely opposed and slid over the ends 26 of a pin 26'. Crimpsleeves 27, 27' are abutted with flanged section 28 of pin 26. The coils21 are thereby mechanically immobilized by means of a crimp joint ontopin 26'.

Electrical connection to the other electrode elements is accomplished bymeans of an interconnection coil 29, which is crimped to centrallyextending pin 30. This connection is illustrative of the many possiblemethods of connecting terminal ends of coils and connection of adjacentcoils to each other.

Eccentric loop structures are depicted in FIGS. 10A, 10B and 10C. Thiselectrode structure is of particular interest because its size, shapeand flexibility make it uniquely suited for implantation through thesmall (1 cm) tubular working channel 41 of a thoracoscopic port insertedbetween the ribs (normally the 4th to 6th intercostal spaces). For thisspecialized application, the electrode structure does not incorporate areinforcing skeleton. In fact, the flexibility of the coils allow themto be deformed during deployment.

In one embodiment (FIG. 10A) the electrode portion 31 is formed by coils32 that are electrically connected at a common terminal point 33. Thisconnection area is molded over with silicone rubber and accepts the leadbody 34. The distal end of the terminal portion is formed by reinforcedsilicone rubber sheet 35 with slit or hole 36 that provides means forfixation on or near the heart by means of conventional sutures orspecialized surgical staples. Additional fixation may be provided on oneor more of the coils near their proximal ends by molding a silicone boot37 onto the electrode coil. Both fixation procedures can be performedthrough the working channel of the thoracoscopic port. Additional loops32' may be beneficial as shown in FIG. 10B as phantom lines.

The novel structural orientation of the terminal end allows theelectrode 31 to be introduced through the tubular working channel 41 bymeans of a tubular applicator 40 that coaxially passes over the leadbody as shown in FIGS. 10D to 10G. The tubular applicator may be asimple, straight thermoplastic tube of appropriate wall thickness or maypossess a deflected tip to assist the user in controlling electrodeplacement on or near the heart surface. The tubular applicator 40engages terminal point 33 of the electrode portion and compresses coils32 within working channel 41.

Upon passage through the working channel 41, as shown in FIG. 10F, thecoils 32 resume their original form for attachment to the heart 49.Resilient biasing means within the coil elements comprising the loopsmay provide additional biasing force to restore the electrode portion toits unstressed shape within the body.

FIG. 10A' shows an electrode portion formed by an outer loop 38 and aninner linear coil element 39 that replaces the inner loop of FIG. 10A.This modification allows the terminal portion 33' to occupy less volumesince only three coil lines are accepted instead of four. Size reductionallows the lead to be passed through small thorascopy working channelswhich may be important for small adult or pediatric patients. These sametechniques may be applied during minimally-invasive introduction ofconcentric loop electrodes (9A, 9B, 9C, 9C').

In FIGS. 10A and 10B, both ends of the coils are electrically common atthe terminal portion 33. An alternative embodiment (FIG. 10C) depicts anelectrode portion formed by two or more eccentric coils 48 that areelectrically common on their proximal ends 47, but are not electricallyconnected at their distal ends 46. The coils are mechanically connected,however by means of an insulting material 48' such as silicone rubber.In this way, any voltage drop is distributed along the length of thecoil.

Electrode portions like those shown in FIGS. 11A, 11A', 11B and 11C areformed by spatially-isolated coil loops 50 mounted on a reinforcedsilicone rubber skeleton 51 similar to those previously described.Spatial isolation of the loops reduces shock impedance and improveselectric field uniformity during shocks.

The structure in FIG. 11A may be deformed and inserted through theworking channel of a thorascope for minimally-invasive implantation,while the three and four lobed structures shown in FIGS. 11B and 11Ccould be more easily implanted using an open-chest procedure. Ingeneral, it is believed that the loops should be energized from thecentral regions of the structure, as shown. Features described forelectrodes shown in FIGS. 9A to 9C may also be implemented here.

To refine the defibrillation efficacy of the present invention, eachelectrode need not be symmetric. In fact, asymmetry may be advantageousfor the production of favorable field intensity distributions duringattempted defibrillation with electrical shocks. Since LV mass isgreater than RV mass, the LV electrode should probably circumscribe aslightly larger area. Ideally, the size, shape and position of theelectrodes would be optimized to minimize areas of low potentialgradient within ventricular myocardium during defibrillation strengthshocks.

The electrodes in a relaxed state need not be planer. Deflection of theelements in a way to form some concavity, as shown in FIG. 9B', may bebeneficial in conforming to the shape of the heart.

Additionally, the electrode elements, normally electrically common, maybe electrically isolated or may be constructed of materials that producedifferences in the relative resistivity between the elements, therebyfavorably altering the current densities along the electrode face.Segments of insulation along the electrode conductors may also enhanceperformance. Spacing between elements, length of elements, and positionof conductor separation may all combine to influence the efficacy ofelectrodes disclosed by the present invention.

An alternative embodiment of the electrode configuration may include theincorporation of more than two electrodes positioned on the epicardium,or the combination of endocardial catheter electrodes with an epicardialelectrode of the present invention on or near the left ventricle.Electrode polarities could be selected to produce the lowestdefibrillation shock strength requirements.

Having described the invention, many modifications thereto will becomeapparent to those skilled in the art to which it pertains withoutdeviation from the spirit of the invention as defined by the scope ofthe appended claims.

We claim:
 1. A body implantable lead, comprising:an insulated lead bodycontaining an electrically conductive element; a first electricallyconductive element and a second electrically conductive element, eachelement having linear portions, which are collinear and adjacent, andend portions, each of which is arcuate and diverging from a common pointrelative to each other, wherein the linear portions have a commonproximal end electrically connected to the electrically conductiveelement; and a third electrically conductive element and a fourthelectrically conductive element radially connected to the commonproximal end, wherein a distal end of the third element is interposedbetween the linear portion and the end portion of the first element, anda distal end of the fourth element is interposed between the linearportion and the end portion of the second element.
 2. The bodyimplantable lead of claim 1, wherein the third element and the fourthelement are arcuate elongate bodies of equal length.
 3. The bodyimplantable lead of claim 1, wherein the first element and the secondelement are elongate bodies of equal length.
 4. The body implantablelead of claim 1, comprising a first support backing and a second supportbacking, the first support backing coupled to the first element and thesecond element end portions and the insulated lead body, and the secondsupport backing coupled to the third element distal end, the fourthelement distal end and the first element and the second element at thecommon point.
 5. The body implantable lead of claim 4 wherein a siliconepolymer covers at least a portion of where the first element and thesecond element end portions and the insulative lead body are coupled tothe first support backing; and where the silicone polymer covers atleast a portion of where the third element distal end, the fourthelement distal end and the first element and the second element at thecommon point are coupled to the second support backing.
 6. The bodyimplantable lead of claim 4, wherein the first support backing and thesecond support backing are each a reinforced silicone rubber sheet. 7.The body implantable lead of claim 4, wherein the first support backingand the second support backing are each a fabric sheet.
 8. The bodyimplantable lead of claim 1, wherein the first element, the secondelement, the third element and the fourth element are each anelectrically conductive coil electrode.
 9. The body implantable lead ofclaim 8, wherein the electrically conductive coil electrode includes aninterior surface defining an interior space which extends along alongitudinal axis of the electrically conductive coil electrode, whereinthe interior space includes a biasing means to maintain structuralstability of the electrically conductive coil electrode.
 10. The bodyimplantable lead of claim 9, wherein the biasing means includes a springwire.
 11. The body implantable lead of claim 9, wherein the biasingmeans includes a silicone member.